The fabrication of some devices often requires protective layers for surface protection and pattern delineation. Such surface layers are useful during fabrication as well as on completed devices. Requirements for such films differ widely depending on the particular fabrication procedure, material, etc. Usually, adherence, stability (particularly toward moisture), and effectiveness as a diffusion barrier are of principal importance. Also, stability, adherence, etc., at high temperatures are desirable where high temperatures are used during fabrication of the device or on subsequent use of the device. In addition, with some applications and fabrication procedures, it might be advantageous for the protective layer to be at least partially transparent to radiation including radiation in the infrared, visible, ultraviolet, X-ray and gamma ray regions.
Optical devices are becoming of increasing importance commercially, principally because of the development of optical communications systems and certain types of display systems. Because of these developments, various optical devices including semiconductor optical devices are becoming increasingly important so that economic and effective techniques for manufacturing such devices are in great demand. Coatings that are suitable for use on optical devices including semiconductor optical devices are highly desirable. Such coatings should be stable, unaffected by ordinary atmosphere substances such as moisture, chemicals, etc., adherent and be able to withstand temperatures used to fabricate the devices or in the use of the devices. Such glass coating should also be readily removable by a convenient procedure. In many devices, the coating should also be transparent at various parts of the radiation spectrum. Where the coating is used to encapsulate optical devices, it should be transparent to the part of the radiation spectrum where they operate. Exemplary optical devices are light-emitting diodes, lasers and optical detectors. The coatings may also be used as reflection coatings to increase or decrease reflection of radiation on the surface of semiconductor optical devices. Indeed, in a general sense, the thickness and optical properties of a glass layer can be adjusted to either increase transmission of the device (e.g., for light-emitting diodes or optical detectors) or increase the reflectivity of the coatings (e.g., for laser applications, etc.).
It should be remarked that the term "optical" is used in a broad sense and is not limited to only visible radiation. The term optical radiation refers to any useful radiation and includes, in addition to visible radiation, infrared radiation, ultraviolet radiation, X-ray and gamma ray radiation, etc.
In the fabrication of some devices it is advantageous to have protective layers that are transparent to radiation. For example, it might be advantageous to observe the surface under the protective layer during processing or at various steps during the processing.
Typical semiconductor devices are described in a variety of references including Light-Emitting Diodes by A. A. Bergh and P. J. Dean, Clarenden Press, 1976 and Injection Electroluminescent Devices by C. H. Gooch, John Wiley and Sons, New York, 1973. Other useful references include Semiconductors and Semimetals, edited by R. K. Willardson and A. C. Beer, Academic Press, 1966, Vol. 2; Physics of III-V Compounds, and Physics of Semiconductor Devices by S. M. Sze, Wiley-Interscience, New York, 1969. These references contain descriptions of various devices including semiconductor lasers, optoisolators, light-emitting diodes, light detectors, solar cells, etc.